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        <span>解决 SpringCloud Fegin 无法传递参数的问题</span>
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                <a href="/2018/04/13/3733447055/">解决 SpringCloud Fegin 无法传递参数的问题</a>
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                <a href="/tags/SpringCloud/">SpringCloud</a>
                
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                <i class="fa fa-calendar"></i> 2018-04-13
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                    <a href="/2018/04/13/3733447055/">解决 SpringCloud Fegin 无法传递参数的问题</a>
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                <i class="fa fa-calendar"></i> 2018-04-13
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                <a href="/tags/SpringCloud/">SpringCloud</a>
                
                
                
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        <p>在看教程的时候发现，平时使用springMVC习惯不加注解。会在springCloud中引起大麻烦</p>
<p>基于微服务的四大基本原则：</p>
<ol>
<li><p>基于AFK拆分原则</p>
</li>
<li><p>无状态服务</p>
</li>
<li><p>前后分离</p>
</li>
<li><p>基于Restful API接口</p>
</li>
</ol>
<p>其中由于是基于Restful 接口，所以不指定@RequestMapping的提交方式是不行的</p>
<p>并且交给SpingMVC自动推断属性名也是不行的 @RequestParam（value=”xxx”） （省略写法 @RequestParam（”xxx”））是必须的</p>
<p>以前写controller层的时候都是默认带上 @RequestParam 的， 今天发现不加 @RequestParam 也能接收到参数</p>
<blockquote>
<p>如果要@RequestParam为一个int型的数据传值，假如前端并未输入，那么将会为int型的数据赋值为null。<br>显然，这是不允许的，直接报错。<br>可以通过required=false或者true来要求@RequestParam配置的前端参数是否一定要传</p>
</blockquote>
<p>下面我们来区分一下加与不加的区别</p>
<p>这里有两种写法</p>
<figure class="highlight java"><table><tr><td class="code"><pre><span class="line">    <span class="meta">@RequestMapping</span>(<span class="string">"/list"</span>)  </span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">test</span><span class="params">(@RequestParam  Long parentId)</span> </span>&#123;  </span><br><span class="line">          </span><br><span class="line">    &#125; </span><br><span class="line">``` </span><br><span class="line"></span><br><span class="line">``` java</span><br><span class="line">    <span class="meta">@RequestMapping</span>(<span class="string">"/list"</span>)  </span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">test</span><span class="params">(Long parentId)</span> </span>&#123;  </span><br><span class="line">          </span><br><span class="line">    &#125; </span><br><span class="line">``` </span><br><span class="line"></span><br><span class="line">第一种 必须带有参数,也就是说你直接输入 localhost:<span class="number">8080</span>/list 会报错 不会执行方法 只能输入 localhost:<span class="number">8080</span>/list?parentId=? 才能执行相应的方法</span><br><span class="line"></span><br><span class="line">第二种 可带参数也可不带参数  就是说你输入 localhost:<span class="number">8080</span>/list 以及 localhost:<span class="number">8080</span>/list?parentId=?  方法都能执行</span><br><span class="line"></span><br><span class="line">当然你也可以设置 <span class="meta">@RequestParam</span> 里面的required为<span class="keyword">false</span>(默认为<span class="keyword">true</span> 代表必须带参数) 这样就跟第二种是一样的了</span><br><span class="line"></span><br><span class="line">如下:</span><br><span class="line"></span><br><span class="line">``` java</span><br><span class="line">    <span class="meta">@RequestMapping</span>(<span class="string">"/list"</span>)  </span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">test</span><span class="params">(@RequestParam(required=<span class="keyword">false</span>)</span>  Long parentId) </span>&#123;  </span><br><span class="line">        .....  </span><br><span class="line">    &#125;</span><br></pre></td></tr></table></figure>

<p>当然你还可以设置里面的defaultValue的属性<br>如下:</p>
<pre><code class="java"><span class="meta">@RequestMapping</span>(<span class="string">"/list"</span>)  
<span class="function"><span class="keyword">public</span> String <span class="title">test</span><span class="params">(@RequestParam(defaultValue=<span class="string">"0"</span>)</span>  Long parentId) </span>{  
    .....    
}  </code></pre>
<p>这样在地址里面也可以不带参数，如果带了参数会接收，不带参数会默认为0</p>
<p>里面还有一个value属性也讲一下， 前面所有的方法 传入的参数必须为parentId 才能接收到值</p>
<p>但是如果你加了value属性</p>
<pre><code class="java"><span class="meta">@RequestMapping</span>(<span class="string">"/list"</span>)  
<span class="function"><span class="keyword">public</span> String <span class="title">test</span><span class="params">(@RequestParam(value=<span class="string">"id"</span>)</span>  Long parentId) </span>{  
    ..  
}  </code></pre>
<p>这样会用id 代替parentId  也就是说你地址里面传入的参数名称为id　localhost:8080/list?id＝？　这种</p>

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    hs.captionEval = "this.thumb.alt";
    hs.numberPosition = "caption";
    hs.align = "center";
    hs.transitions = ["expand", "crossfade"];
    hs.lang.number = '共%2张图, 当前是第%1张';
    hs.addSlideshow({
      interval: 5000,
      repeat: true,
      useControls: true,
      fixedControls: "fit",
      overlayOptions: {
        opacity: 0.75,
        position: "bottom center",
        hideOnMouseOut: true
      }
    })

    // 初始化aos
    AOS.init({
      duration: 1000,
      delay: 0,
      easing: 'ease-out-back'
    });

</script>
<script>
	POWERMODE.colorful = 'true';    // make power mode colorful
	POWERMODE.shake = 'true';       // turn off shake
	// TODO 这里根据具体情况修改
	document.body.addEventListener('input', POWERMODE);
</script>
<script>
    window.slideConfig = {
      prefix: '/imgs/slide/background',
      ext: 'jpg',
      maxCount: '6'
    }
</script>
<script src="/js/hs.js"></script>
<script src="/js/blog.js"></script>



</html>